Weak high pressure is affecting the area and dust will be observed in the atmosphere, the met office said in its early morning weather bulletin.
Monday will be mainly fine, with increased cloud at intervals in the mountains in the afternoon.
Temperatures will be 30 C inland, 27 C on the east coast, around 25 C on remaining coasts and 22 C in the mountains.
Tonight will be mainly fine. Temperatures will fall to 15 C inland and the west and north coasts, around 16 C on the east coast and 12 C in the mountains.
Tuesday and Wednesday will be mainly fine with increased cloud at intervals.
On Thursday increased cloud may lead to local showers while isolated thunderstorms are possible in the afternoon in the mountains and inland.
Temperatures are expected to remain at the same levels over the next three days, remaining above average for the time of year.